Electronic surveillance measurement (ESM) receivers commonly require that frequency calculations be performed on a received signal from targets of interest. The frequency of an input signal is often measured using an instantaneous frequency measurement (IFM) receiver. The IFM receiver, generally, uses a difference in phase between a delayed and a non-delayed version of an input signal to calculate the frequency of the input signal.
The IFM receiver may cover a wide input frequency range such as, for example, a range from 2 GHz to 18 GHz. The receiver may process short pulse widths and obtain good frequency accuracy. A conventional IFM receiver may be built through analog means with frequency correlators. The advancement in digital signal processing techniques has resulted in IFM receiver approaches with a one bit digitized signal. An example of an IFM receiver with a one bit digitized signal is disclosed in U.S. patent application Ser. No. 11/170,121, filed on Jun. 29, 2005, which is incorporated herein by reference in its entirety for its teachings on instantaneous frequency measurements.
It is important to be able to confirm that the measurement of frequency by an IFM receiver is correct. Presently, IFM receivers do not do this directly, but rather, try to detect a variety of conditions that could lead to an incorrect measurement. An example of an IFM receiver with frequency confirmation is disclosed in U.S. patent application Ser. No. 11/270,096, filed on Nov. 9, 2005, which is incorporated herein by reference in its entirety for its teachings on instantaneous frequency measurements and its subsequent frequency confirmation.
The present invention provides another technique for directly confirming the frequency measurement of a signal received by an IFM receiver. In addition, the present invention provides a technique for measuring the width of a pulse received by the IFM receiver and also estimating the time-of-arrival (TOA) of that pulse.